1. Field of the Invention
The present invention relates to an engine valve mechanism and more particularly to a valve actuating mechanism for an internal combustion engine. More specifically, the present invention pertains to an engine valve actuating mechanism which can hold engine valves in closed positions so as to make an engine cylinder inoperative when desired.
2. Description of Prior Art
Efforts have hithertofore been made to develop valve actuating mechanisms by which engine intake and exhaust valves can be held in closed positions so that one or more cylinders of the engine are made inoperative under certain engine operating conditions, for example, under a light load engine operation. For the purpose, the British Pat. No. 1,275,328 proposes a valve actuating mechansim including a rocker arm device which is comprised of a cam actuated arm and a valve actuating arm, both of the arms being mounted on a shaft for swingable movement with respect to each other about the axis of the shaft. The cam actuated arm is engaged with a valve actuating cam so that the arm is swingably actuated by the cam. The cam actuated arm carries a hydraulically actuated plunger having one end engaged with the valve actuating arm which is adapted to operate an engine valve. An application of a hydraulic pressure to the plunger causes the plunger to restrict the relative swingable movement between the arms so that a movement applied by the cam to the cam actuated arm is transmitted through the plunger to the valve actuating arm to thereby actuate the engine valve. When the hydraulic pressure is released, the movement of the cam actuated arm is no longer transmitted to the valve actuating arm so that the engine valve is maintained in the closed position.
The proposed mechanism is however considered disadvantageous in that the cam actuated arm must be formed with a hydraulic cylinder for slidably and liquid-tightly receiving the plunger. Further, hydraulic liquid passages must be formed in the cam actuated arm and the shaft carrying the arm. Thus, the proposed mechanism is complicated in structure and expensive to manufacture. It should further be pointed out that the mechanism shows a poor responsive characteristics in switching between the motion transmitting condition and the free condition since the switching is performed hydraulically.
Japanese laid open utility model 57-193903 proposes an engine valve actuating mechanism in which the rocker arm device is comprised of a cam actuated arm and a valve actuating arm which are swingably mounted on a shaft. The cam actuated arm is further slidable along the shaft so that it can be moved between an engaged position wherein it is engaged with the valve actuating arm and an axially shifted, disengaged position wherein it is disengaged from the valve actuating arm. The proposed mechanism is however disadvantageous in that a complicated mechanism is required for moving the cam actuated arm between the engaged and disengaged positions. Further, the cam actuated arm must be of a substantial axial length so that it can be maintained in engagement with the valve actuating cam both in the engaged and disengaged positions.